At one time, in the construction of commercial and residential buildings and the like, the frames around doors were custom made and erected by carpenters, and the like, and the erected door frames were then hand painted by professional painters. This method of construction was labour intensive and hence costly.
More recently, to reduce labour content, pre-fabricated pre-finished door frame assemblies have become popular. Such frame assemblies, while having the advantages of being pre-finished with one or more of an assortment of finishes such as woodgrain or paint surfaces, and being readily erectable, nevertheless suffer from certain deficiencies. One deficiency is that the width of the door jamb is fixed, and hence the pre-fabricated door frame only fits a wall of a given thickness. Consequently, if there is much variation in wall thickness in comparison with the dimensions of the door frame, the door frame is not satisfactory, and another door frame assembly of the required jamb width is required. Right hand and left hand doors also create difficulties. Accordingly, rejections at the construction site frequency occur and replacement door frame assemblies must be supplied, thereby increasing costs of construction.
Relatively recently, several Canadian patents have been granted for door frame assemblies which have hinge, strike, and header jambs, that can be varied in width to accommodate different thicknesses of walls. Canadian Pat. Nos. 983,321, issued Feb. 10, 1976, 1,020,810, issued Nov. 15, 1977 and 1,032,018, issued May 30, 1978, each granted to Eldon W. Carmichael, disclose several types of door frame assemblies which can accommodate different wall thicknesses. However, the door frame assemblies disclosed and claimed in these patents incorporate a number of features which appear to detract from the utility of the door frame assemblies in certain construction situations. The Carmichael door frame assemblies as part of the variable width jamb feature, utilize a slide guide which is constructed with springs or with a tongue and groove arrangement, both of which constructions are relatively expensive and hence unsuitable for certain construction jobs.
Once a variable jamb width door frame assembly is in place in the opening through a wall, the width of the jamb is fixed and need not be adjusted further. Accordingly, a slide guide equipped with a spring is of marginal benefit. While the presence in the slide guide of a spring under tension tends to hold the side moldings of the door frame snug against both sides of the wall, such springs are apparently not absolutely necessary in order to provide an attractive appearance to the erected door frame. Similarly, a tapered tongue and groove slide guide assembly, while being of some utility in holding the components of the door jambs in planar alignment, is not of much assistance in holding the components in vertical alignment (when one considers the erected frame assembly) because the tapered tongue and groove construction, by reason of its design, particularly when it is in extended orientation, permits a certain amount of "play" to occur in the slide guide. Hence, one jamb component can be moved upwardly or downwardly in relation to the other jamb component. Furthermore, the Carmichael door frame assemblies, by design, utilize mitred frame corners, which tend to be costly to produce, and which are somewhat disadvantageous in certain construction situations because a perfectly square corner must be formed in order for the mitred joints to fit closely and give the assemblied door frame a good appearance.